Static Wicks

[Jim Lee]

The Czech’s are really into static and lightning protection.  I don’t know why.  Their houses and buildings all have huge cables running up and over and down the other side for lightning protection.  Their planes have static wicks which extend down from the landing gear.

 

When I asked what all of those cables on the roofs were about, they answered “lightning protection” (you idiot).  So I thought, yes, that’s right, whenever there is a lightning storm our houses in the US blow up.  What a cynic I am.

 

So what does the static wick on a Phoenix do anyway?  Well, presumably, it is to prevent a fire or explosion when fueling the plane.  You know, to prevent what happens to our planes in the US without static wicks when we refuel; they blow up, right?  How many Pipers or Cessnas have you seen with static wicks which drag the ground?

 

The one thing that I do know for certain is that when the static wick drags on the ground, it stabs the tire and creates flats.  I had a lot of them for no reason until I guessed that the wick was creating the flats and chopped mine off shorter to where it wouldn’t drag on the ground, but would maybe strike the ground on landing (when the tire gets squished just a little).  No more flat tires!  (Except for the ones with thorns in them).

 

One major difference between the US and the Czech Republic is that we almost always fuel up at a pump with a grounding wire attached to the engine, and in Czech, they mostly fuel from gas cans.  So without a grounding wire or some way to prevent a static discharge when you fuel with a can,  maybe there is a higher risk of fire or explosion.

 

Phoenix Air does a really good job with the static wicks.  They screw into the gear leg, contacting a wire which is inside the gear leg, and runs into the cockpit and attaches to the flight controls, which are connected to the engine and all other metal parts in the plane.  There is also a wire which runs from the gas cap inside the fuel tank to the fuel sensor wires which are also grounded to the rest of the plane.

 

I think most static charges are created by the plane flying through the air.  If this is true, the most dangerous time to fuel the plane is right after landing.  Just because you hook up the grounding wire at the fuel pump, does that mean the gas nozzle touching the metal edge of the gas filler on the plane won’t create a spark?  It makes sense to me that a fuel pump has a grounding wire which is well and truly grounded into mother earth.  But what about the connection from the metal gas filler on the wing to the grounding wire?  Just how good of a connection is that in most planes?  (Aircraft certified for IFR flight have to have static wicks on control surfaces and other special precautions for lightning protection).  Should we be touching the gas nozzle to the grounding wire station before taking it to the plane?

 

I don’t think a plane gets a static charge by sitting in the hangar.  We all know that scuffing our feet across a carpet creates static electricity.  But I have yet to get a static discharge from walking around on the pavement or concrete around my hangar, ever, that I can recall.  Having worked just a little with circuit boards, I know that you must be careful and touch a metal table before working on the circuit board to prevent damage due to static discharge.  But what about a plane sitting on concrete, with the gas boy (me) wearing rubber soled shoes, holding a plastic container with a plastic spout, and pouring gas into the Phoenix?  Does the static wick reduce the risk of fire?  How much risk of fire is there?

 

I know of one guy who was draining fuel from his high wing Cessna into a pan sitting on the floor; a 6 foot drop or so.  And the pan of fuel caught fire presumably from the fuel dropping that far into the pan, and burned up the plane.

 

What about fueling our cars?  I know not to talk on the cell phone, or get in and out of the car while fueling, or fill gas cans while they are inside the car, and things like that.  But with the billions of auto fueling events each year with maybe a couple of fires here or there (caused by smokers?), what is the real danger?

 

Does the wick need to drag on the ground?  Is it ok if it just touches during the landing?  Can we just remove them entirely?  Do I need to make a grounding wire attached to the metal hangar and use that just like we do at the pumps?

 

There are a lot of very smart Phoenix owners out there.  After all, they bought a Phoenix instead of something else, right?  If someone can chime in on this subject (Martin?  Eric?  Ivan?) I would appreciate it.

[Eric Greenwell]

I did some internet research and found nothing definitive about static wicks or tire conductivity. The consensus seemed to be ...

• Fill the cans only on the ground, pavement, or floor
• DO NOT fill when they are in the trunk or pickup bed
• There is no evidence that using cell phones can cause a fire, nor would I expect a low voltage (3.7 volt battery), low power device to have any way to do that (a battery that fails and ignites - yes, but that doesn't happen because you used it!)

The conductivity of airplane tires was not mentioned much. Using a grounding lead in the hangar would ensure the Phoenix is grounded, but I'm willing to believe the aircraft will not have a charge after sitting in the hangar for a few minutes, that the gas cans sitting on the floor will not have a charge, and that I will not have charge after opening the door to the hangar; therefore, it's safe to set a can on the wing and empty it into the fuel opening. Our area is dry enough to give me static electricity when I slide out of my Camry's cloth seats in the winter, but that's always discharged by touching or holding onto the car.

I do use cans that don't spill gasoline, and are very easy to use on the Phoenix. Ed Walker put me onto them: search Amazon for "no-spill gas cans". Just set it on the wing with nozzle in the fuel opening, press the button on the nozzle, and in it goes, with automatic stop should the fuel reach the nozzle. A bargain at $34 with shipping (Ace Hardware has them for the same price in the store).

I hope someone can be more definitive.